Thermoplastic elastomers are known. They have many of the properties of thermoset elastomers, yet they are processable as thermoplastics. One type of thermoplastic elastomer is a thermoplastic vulcanizate, which may be characterized by finely-divided rubber particles dispersed within a plastic matrix. These rubber particles are crosslinked to promote elasticity.
For example, U.S. Pat. No. 6,750,292 teaches thermoplastic vulcanizates that include a semi-crystalline polyolefin, a rubber that is at least partially vulcanized, and an oil. The oil is characterized by low aromatic content (less than 4 weight percent), and has a viscosity of at least 85 cSt (and preferably 90-25 cSt) as measured at 40° C. The oil to rubber (e.g., EPDM) ratio is from 0.7 to 2.0, and preferably between 1.3 and 1.6.
Because thermoplastic vulcanizates have many advantageous characteristics including processability, ease of fabrication, and useful mechanic and dynamic properties, thermoplastic vulcanizates are widely used. In particular applications, thermoplastic vulcanizates are used in applications where they are in contact with water, particularly potable water. As a result, these articles often must meet governmental standards for microorganism growth (i.e., give rise to less than threshold amounts of microorganism growth). Inasmuch as thermoplastic vulcanizates are hydrocarbon-based, the ability to meet these governmental standards is not trivial.